A nut or bolt head may be tightened by a power torque wrench while transferring the counteracting reaction torque onto a washer beneath that nut or bolt head. This provides for a balanced, localized overall torque transfer that is self centering and does not require the need to manually oppose the actuation torque or support the power torque wrench eccentrically via a reaction member. It has been first described and claimed in a Japanese Patent Application and following U.S. Pat. No. 3,581,383. Reaction washers commercially available at the time of this invention are direct representations or obvious variations there from.
A reaction washer transfers the received reaction torque onto a resting surface beneath. From the resting surface, the reaction torque is transferred onto a thread hole, bolt or thread stud via which it counteracts the actuation torque exerted on the tightening element as is well known in the art. To avoid slipping and effectively transfer the reaction torque onto the resting surface, reaction washers commonly employ serrations on its bottom to bite into the resting surface. In order for these bottom serrations to bite, a contact force must be induced during initial tightening that is large enough for a given overall contact area of the bottom serrations to penetrate into the resting surface. Only then, the reaction washer won't slip and spin when the power tool starts to apply torque to the nut and/or bolt head while withholding itself via a concentric reaction socket on the reaction washer.
The friction on the reaction washer top has to be substantially lower than on the reaction washer bottom to prevent the reaction washer to be rotated with the nut instead of biting into the resting surface during initial manual tightening. This is particularly problematic in real world applications where the resting surface may be coated with oil or paint for corrosion protection. To keep the friction at the washer top to a minimum, it is commonly made smooth and hard, which bears the risk of the nut or bolt head becoming inadvertently loose. This substantially reduces the feasibility of prior art reaction washers for securing nuts and bolt heads. Moreover, the employment of additional well known safety washers in between the nut or bolt head and the reaction washer is prohibitive as it might cause the reaction washer to be dragged along during initial tightening instead of biting into the resting surface. Therefore, there exists a need for a reaction washer that maximizes bite at its bottom and provides low friction on its top during initial tightening and that secures the nut and/or bolt head after fully tightening it. The present invention addresses this need.
Reaction washers commonly feature a circumferential spline via which the reaction torque is radially transferred by a reaction socket that encompasses the reaction washer when coupled together. The radial torque transfer results in substantial radial forces especially in case of a loosely coupling wave shaped spline as is common in prior art reaction washers. To withstand those radial forces, the reaction socket has to have a substantially larger outer diameter at its bottom, which in turn increases the required clearance around the nut and/or bolt head to be tightened or loosened via a reaction washer. Also, debris and eventual paint tends to accumulate in the bottom corner around the reaction washer and the resting surface. This reduces the accessibility of the circumferential reaction washer spline particularly during loosening when increased reaction torque may need to be applied for snapping free the nut and/or bolt head. Further more, the shallow reaction washer spline of prior art reaction washers bears the risk of the reaction socket to snap off particularly during peak torque transfer were the spline and reaction socket may elastically deform. Therefore there exists a need for a reaction coupling of a reaction washer that does not produce substantial radial forces in the reaction coupling, that provides for a reaction coupling outer diameter at its bottom that does not exceed the outer diameter of the reaction washer, that is insensitive to eventual debris and/or paint accumulation along the outer bottom contour of the reaction washer and that provides for a secure axial coupling of the reaction socket to prevent it snapping off during peak torque transfer. The present invention addresses also this need.
Corrosion, paint and/or debris may impair a snug fit between the reaction washer and the reaction socket to the extent that the required reaction torque for loosening the nut and/or bolt head cannot successfully be transferred any more. Therefore, there exists a need for an axially reacting washer stack system that covers the reaction coupling. The present invention addresses also this need.
The circumferential spline of prior art reaction washers can be accessed from both axial sides of the reaction washer. Consequently, such prior art reaction washers may be inadvertently assembled upside down with the bottom serrations engaging with the nut and/or bolt head while the smooth reaction washer top comes in contact with the resting surface. Inadvertent inverted assembly of reaction washers makes them inoperative. Therefore, there exists the need for a reaction washer and/or axially reacting washer stack with reaction coupling configuration that can be axially accessed only from one intended side thereby eliminating unintentional wrong positioning of it. The present invention addresses also this need.
With increasing bolt diameter and/or elastically deflecting resting surfaces, the initially established axial force during manual pre tightening is commonly insufficient for the bottom serrations to bite. As an unfavorable result, in real world applications of large sized nuts or bolts with eventually oiled, coated and/or elastically deflecting resting surfaces, prior art reaction washers tend to slip during initial power assisted tightening. Therefore, there exists a need for a reaction washer integrated in or combined with an axially reacting washer stack that in response to an initially receiving reaction torque automatically ramps up axial contact force at the begin of power tool induced tightening and thereby secure sufficient bite into the resting surface. The present invention addresses also this need.
Bolts and nuts commonly experience a substantial increase of friction coefficient in their main threads between tightening and loosening of them. This may be caused by corrosion, heat induced coking of lubricant and/or galing of the main thread as is well known in the art. The torque required to loosen loaded nuts and bolts having increased thread friction may exceed structural limits of the bolt shaft and/or of the actuation coupling of the nut or bolt head making it impossible to disassemble it nondestructively. Therefore, there exists a need for a reaction washer integrated in or combined with an axially reacting washer stack that receives a reaction torque and automatically axially ramps down the axial load and related load friction in the main thread on tightened nuts and/or bolts during initial power tool induced loosening of them. The present invention addresses also this need.
Prior art direct tension indicating washers are employed and very practical to identify and inspect whether or not a nut and/or bolt head has been tightened in general and tightened with a minimum required torque in particular. As reaction washers are very convenient for tightening and/or loosening nuts and/or bolt heads, there exists a need for a reaction washer integrated in and/or combined with a reacting washer stack that provides also direct tension indication. The present invention addresses also this need.